An Eastern Egg Rock Atlantic puffin carries white hake to its fledglings. White hake is long and narrow compared to the butterfish.

Eastern Egg Rock is a freezing speck of island that clings to the coast of Maine, north of Boston. It is fringed with a few bushes, has little soil and no supplies of fresh water. Yet this unprepossessing, seven-acre scrap of wave-washed granite is a site of major ecological interest. Thanks to research carried out here, scientists are gleaning invaluable – and alarming – data about the impact of climate change on the planet’s wildlife.

The project is the work of Steven Kress, a veteran ornithologist who constructed a sanctuary here for the Atlantic puffin 35 years ago. The puffin (Fratercula arctica), distinguished by its parrot-like, red-and-yellow bill, had been wiped out there by hunters in the 19th century. In the 1970s, Kress decided to bring them back.

“Puffins are monogamous, loyal and great providers for their young,” says Kress. “I was smitten by them.”

Some starve to death even though their parents are bringing them plenty of fish

Reintroduction was no easy task, however. The puffin is also a highly social bird and usually returns to its parents’ colony to breed after spending several years at sea. “We had to find a way to persuade them to settle on Eastern Egg Rock instead, ” says Kress.

The solution, he decided, was to use puffin decoys in the same way that wildfowl hunters employ decoys to attract duck and geese to their guns. One-foot-high wooden replicas were peppered round the island to entice young puffins to land, socialise and eventually breed with other curious puffins. After several years, Kress and his team succeeded, establishing a puffin colony on Eastern Egg Rock in 1981. It is one of only a handful of spots in the US where the species nests.

“At the time, our decoy plans were scoffed at. However, we succeeded to the extent that the technique is used today round the world to attract birds to new colonies. It is not so much the colour of the decoy that was important we found but the accuracy of its silhouette.”

In 1987, Kress was given a Rolex enterprise award for his efforts. This came with a grant of 50,000 Swiss francs which he used to extend his programme to other seabirds and other parts of the world. Today, there are around 1,000 pairs of puffins on Eastern Egg Rock and other islands nearby.

It is a remarkable success story. However, scientists working at the colony, which is supported by Audubon Society, have recently uncovered a worrying trend – a decline in puffin fledgling survival rates. Kress explains: “Most seabirds catch fish and then regurgitate them to feed their young. However, puffins drape the fish that they catch over their beaks before dropping them into the mouths of their chicks. They are like little fishing fleets going out every day before coming back with their catch of the day. Crucially, it is very easy to identify what they have caught. You can see it hanging from their beaks.”

This is the ocean’s equivalent of the canary in the coal mine

Because of this, Kress’s team have been able to study puffin diets in detail for several decades – and found the birds usually fed on hake and herring. Recently, however, there has been a change in puffin diet on Eastern Egg Rock. Herring has disappeared from the menu. Instead, parents are bringing home supplies of butterfish to the nest – with disastrous consequences.

“Butterfish are much rounder and much more difficult to eat,” says Kress. “Essentially the chicks cannot swallow them and some starve to death even though their parents are bringing them plenty of fish.”

Many chicks still make it to adulthood but suffer seriously reduced body weights which leave them less able to withstand the vicissitudes of sea life. Using data records for the past 20 years, Kress and his team calculate that fledging survival rates have declined by an average of 2.5% per year for those two decades.

As to the cause of this harmful change in diet, Kress points to the dangers posed by climate change. “As the Arctic heats up, seas in higher latitudes are getting warmer and warmer. As a result, populations of fish that normally thrive in more southerly waters are moving into these more northerly waters.”

The butterfish is an example and it is having a real impact on the puffin. Their chicks can only fit smaller, narrower fish, such as white hake –into their beaks and they have trouble swallowing larger, oval-shaped species like butterfish. The problem is made worse because puffin parents don’t tear up or partially digest the fish they catch for their young. “There is a YouTube clip of a young puffin trying, and failing, to swallow a butterfish,” said Kress. “The tragedy is that the puffins are surrounded by plenty of fish. This is the ocean’s equivalent of the canary in the coal mine. It’s telling us that climate change will not just affect the distribution of fish round the world but there could be disastrous consequences for many different species of wildlife that depend on these fish for food, such as the puffin.”